The focus of this research project is to investigate a novel level of cross-talk between the TNF-alpha and IFN-gamma signaling pathways in macrophages and microglia. IFN-gamma and TNF-alpha synergize in the production of a large number of pro-inflammatory cytokines, chemokines, and co-stimulatory molecules and are potent activators of macrophages and microglia. Cross-talk between these two signaling pathways is thought to occur at the promoter level by the binding of transcription factors independently activated by these two pathways. Other levels of cross-talk/coordination became apparent when I made the observation that TNF Receptor 1 associated death domain protein (TRADD) and Signal Transducer and Activator of Transcription(STAT-1), signaling components of the TNF-alpha and IFN-gamma signaling pathways, respectively, are induced to physically associate with one another upon exposing cells to IFN-gamma. These observations led to the hypothesis that, in addition to the interaction at the level of transcription factors at the promoter level, there are other levels of interaction between these two pathways that may play an important role in regulating the response of cells to these cytokines. To test this hypothesis, two Specific Aims were formulated in an attempt to define regulation and function of the TRADD:STAT-1 complex: First, to define the regulation and sub-cellular localization of the STAT-1:TRADD complex, and second, to determine the function of the TRADD:STAT-1 complex and investigate a potential role of TRADD in IFN-gamma signaling. These studies may elucidate novel mechanisms of macrophage/microglia regulation.